Control apparatus and method for transporting sheets

ABSTRACT

An apparatus and a method for controlling the correct transport of sheets. The thickness of one or several superimposed sheets is sensed to determine how many sheets are simultaneously transported. Transducer means transform mechanical magnitude signals into signals having a different physical quality, for example electric signals, and the transformed signals are evaluated and supplied by an output selector to different outputs which are, respectively, correlated with different numbers of sensed superimposed sheets.

United States Patent 1191 Fiirster et a1.

11] 3,826,487 1451 July 30, 1974 CONTROL APPARATUS AND METHOD FORTRANSPORTING SHEETS Inventors: Karl-Heinz Fiirster, Dresden;

Lothar Vetter, Radebeul; Helmut Stange, Dresden, all of Germany VEBPolygraph Leipzig, Leipzig, Germany Filed: Jan. 24, 1972 Appl. No.:220,204

Assignee:

us. c1. 27l/263,33/l47 L, 33/DIG. 13, 73/377, 340/259 1m. 01 B65h 7/04Field of Search 271/57, 47; 73/377, 37.5; 33/148 H, 147 L, 010. 13;340/259 References Cited UNITED STATES PATENTS 4/1946 Agnew et a1.33/147 L 2/1955 Zugel et :11 271/57 X 3,176,981 4/1965 Vandeman 271/573,182,301 5/1965 3,194,055 7/1965 Primary ExaminerEv0n C. BlunkAssistant ExaminerBruce H. Stoner, Jr. Attorney, Agent, or FirmMichaelS. Striker 5 7 ABSTRACT An apparatus and a method for controlling thecorrect transport of sheets. The thickness of one or severalsuperimposed sheets is sensed to determine how many sheets aresimultaneously transported. Transducer means transform mechanicalmagnitude signals into signals having a different physical quality, forexample electric signals, and the transformed signals are evaluated andsupplied by an output selector to different outputs which are,respectively, correlated with different numbers of sensed superimposedsheets.

12 Claims, 10 Drawing Figures PATENTED sam aura FIG. /0

PAIENTEB SHEEY 0F 4 0 milk CONTROL APPARATUS AND METHOD FOR TRANSPORTINGSHEETS BACKGROUND OF THE INVENTION The present invention relates to anapparatus and method for controlling and indicating the correcttransport of sheets for detecting the omission of sheets or multiplesheets which are transported and fed to a sheet processing machine.

Arrangements for the detection of double sheets or missing sheets areknown in which the thickness of a sheet is measured at two separatestations, and the difference between the two measured values isrecorded. It is a disadvantage of the known arrangements that, at thestart of a sheet feeding operation, the sensed value is available onlyafter a period of time corresponding to the time of the travel of thesheet between two sensing or monitoring stations. This causes particulardifficulties when the machine is started. Furthermore, difficultiesarise regarding equal adjustment when employing two detecting stations.

The BRD-AS 1,204,243 discloses electromechanical apparatus for the sheetcontrol. It is a disadvantage of this apparatus that the exactadjustment of the contact causes difficulty, and that the contacts aresubject to wear, and therefore unreliable.

The BRD-AS 1,238,492 and BRD-AS 1,092,438 disclose measuring methodrequiring electronic signal processing since they have capacitive orinductive detecting devices.

It is one object of the invention to provide a method and apparatus ofsimple construction capable of detecting improperly fed sheets. Arelated object of the invention is to detect and indicate omitted sheetsand multiple sheets at a point near the sheet separation.

In accordance with the invention, omitted sheets and any number ofsuperimposed sheets sticking together are clearly indicated by specificsignals.

It is also an object of the invention, to provide an apparatus having alarge measuring range and a small sensing pressure, and beingindependent of the properties of the transported sheet materials.

It is also an object of the invention to provide an apparatus and methodwhich can be applied to either separately successively fed sheets or tosheets fed in overlapping condition.

In accordance with the invention, the thickness of sheet meanstransported at a measuring point at a measuring moment is transformedinto an amplitude variation of a signal magnitude sensor, the amplitudevariation is transformed into a signal having a different physicalquality, and the transformed signals are evaluated and supplied to anindicating device and/or registering device, and/or to a machine controldevice.

An apparatus according to the invention comprises thickness magnitudesensor means for sensing transported sheet means and generatingmagnitude signals representing the number of sheet portions of the sheetmeans superimposed at a sensing point; signal transducer means fortransforming the magnitude signals into transformed signals having adifferent physical quality; signal evaluation means for the transformedsignals for representing different sensed thicknesses of the sensedsheet means by different electric signals, respectively; a plurality ofoutputs respectively associated with sheet means of different thickness;and output selector means, such as a multipoint device, receiving theelectric signals and supplying different electric output signals tocorresponding different outputs.

As a result, signals at different outputs represent a missing sheetmeans and different numbers of superimposed sheet portions,respectively, whereby omission of a sheet or multiple sheets can berecognized.

In one embodiment of the invention, a flexible sensing arm, whose freelength is adjustable, is used as a magnitude sensor means, and has anextensible strip whose resistance is varied when the sensing arm isdeflected by sensed sheet means. The extensible strip serves astransducer.

In another embodiment of the invention, a sensing lever is mounted forangular movement, and has a baffle plate cooperating with a pneumaticnozzle of a pneumatic-electric transducer.

In a third embodiment of the invention, photoelectric sensing means areused which indicate displacement of a sensing piston by sheet means ofdifferent thickness by electric signals generated by a photoelectricmatrix.

The multipoint device or output selector has different adjustablethresholds for omitted sheets, properly fed sheets, and any number ofmultiple sheets.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following de scription of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic block diagramillustrating the operational principle of an arrangement according tothe invention;

FIG. 2 is a diagram illustrating voltage potentials of output selectormeans shown in'FlG. 10;

FIG. 3 is a fragmentary side elevation illustrating parts of a firstembodiment of the invention;

FIG. 4 is a fragmentary side elevation illustrating part of the secondembodiment of the invention;

FIG. 5 is a fragmentary side elevation, partially in section,illustrating part of a third embodiment of the invention;

FIG. 6 is a fragmentary front view illustrating a detail of theembodiment of FIG. 5 on an enlarged scale;

FIG. 7 is a diagram illustrating a first signal evaluation device forthe embodiment of FIG. 3;

FIG. 8 is a diagram graphically illustrating a pressure variationoccurring in the embodiment of FIG. 4;

FIG. 9 is a schematic sectional view of a pneumaticelectric transducerfor the embodiment of FIG. 4; and

FIG. 10 is a circuit diagram illustrating an output selector meansparticularly suited for the embodiment of FIGS. 3 and 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS When a stream of successivesheets are transported along a guide table, it is possible to transportseparate single sheets, or to arrange successive sheets in overlappingposition, as shown for sheets 1, l in FIGS. 3, 4 and 5. The free end ofthe sheet 1 again overlaps with another sheet, not shown. It is possiblethat a sheet is omitted or that several sheets together are transportedas if they were a single sheet.

In accordance with the invention either the separate sheets, or theoverlapping portions of successive sheets are sensed and the lack of asheet and sensed thickness of more than two overlapping portions of twosuccessive sheets, indicates the improper transport of two or moresheets which stick together.

Referring now to FIG. 1, the thickness of a sheet means 1, or 1,1 or ofa multiple sheet, is measured at a measuring point by a detector 7 whichincludes a thickness and magnitude sensor means 8, and a signaltransducer means 9. The thickness of the sheet means 1, as schematicallyindicated in FIG. 1, is determined by the detecting means 7 which restswith a small measuring pressure 2 on the sheet means 1. The magnitudesensor-means 8 is placed in the sensing position by a conventionalcyclic control device 3 so that the overlapping sheet portions aresensed by sensing rollers 22 or 22 as shown in FIGS. 3 and 4 only atpredetermined time intervals.

The magnitude sensor means 8 includes a signal range adjuster 4. Thethickness representing magnitudesignals of the detecting means 7 andmagnitude sensor means 8, are supplied to signal transducer means 9 inwhich the magnitude signals are transformed into signals havingadifferent physical quality; forexample, mechanical displacement of thesensing arm 21 with sensing roller 22 in the embodiment of FIG. 3 istransformed into a resistance change of an expansible strip 9.

The transformed signals (e.g. the resistance changes of strip 9)produced by the signal transducer means 9 are supplied to signalevaluating means 10-which includes a zero point adjusting device whichrepresents a thickness of the sheet means corresponding to a desiredcorrect thickness.

An output selector means or multipoint member 11 receives the signalsfrom the signal evaluation device shown in FIG. 7, for example, andsupplies different electric output signals at corresponding outputs 12to 16 so that the voltage appearing at a particular output representsthe thickness of the sensed sheet means 1, 1'. It will be self-evidentto persons skilled in the art that multipoint member 11 accordinglyconstitutes an analog-to-digital converter; this is also clear from FIG.

2 (discussed below) which sets forth in graphical form the operation ofthe multipoint member 11, this graphical representation being evidentlya representation of the conventional operation of a conventionalanalogto-digital converter. The output selector means 11 is providedwith an adjusting means 6 for setting the device for omitted sheets ormultiple sheets in a known manner. The multipoint member or outputselector means 11 supplies signals to the outputs 12 to 16,respectively, in accordance with the sensed magnitude, and output 12 maybe associated with an omitted sheet, output 13, with a correctlypositioned sheet, output 14 with a double sheet, output 15 with a triplesheet, and output 16 for a stack of four sheets. Further outputs forsheets forming stacks may be provided.

Outputs 12 to 16 are connected with an indicating means 17 and therespective output signals are indicated; for instance, one light bulbcan be provided for each of outputs 12-16. At the same time the outputsl2 and 16 are connected with a registering device 18 where the outputsignals are registered for further processing. The outputs 12 to 16 arealso connected with a machine control means 19, and used for controllingfunctions of a sheet transporting and feeding machine, for example,blocking of the transporting movement and the like.

The devices 17 to 19 may be combined with each other in accordance withspecific conditions at the machine. If the respective devices arecontrolled by different power and energy than the output selector 1!, asystem transducer 20 is connected between the outputs 12-15 and thedevices 17 to 19.

FIG. 3 illustrates a first embodiment of the invention. The detectormeans 7 includes a signal magnitude sensor means 8 including a bendablesensing arm 21 with a sensing roller 22 which rolls on and senses thethickness of the stream of sheets guided along the guide table 23. Thearm 21 is secured in a support 25, which after loosening of theadjusting screw 25a, can be displaced in support 25 for varying thelength of the sensing arm 21 which corresponds to the measuring rangeadjuster 4 of FIG. 1, as indicated in FIG. 3 by the double arrow. 4.Signal .transducer means 9 include an extensible resistor strip 24mounted on the sensing arm 21, and being preferably a semi-conductorextension measuring strip. As noted with reference to FIG. 1, a cycliccontrol device 3 places at the sensing moment the sensing roller 22 inthe correct sensing position.

A signal evaluation means 10 for the embodiment of FIG. 3 is shown inFIG. 7. When sensing arm 21 is elastically displaced and bent,resistance of strip 24 is varied. Resistance strips of this type aresometimes referred to in the art as strain gages. As shown in FIG. 7 twostrips 24 are provided which are connected by a bridge circuit with twoadjustable resistors 26, 27. The bridge outputs form the inlets of thefeedback amplifier 28 whose output Ua is connected with the multipointmember or output selector 11, shown in FIG. 10. The voltage Ua varies inaccordance with the sensed thickness of the respective sheet means 1,1.

The multipoint member or output selector 11 shown in FIG. 10 has a zeroamplifier V for the voltage Ua supplied from the signal evaluationdevice 10 shown in FIG. 7. Transistor switches T1, T2, T3 are connectedin series with resistors R. Depending on the magnitude of the inputvoltage Ua, one of the transistor switches T1, T2, T3 is operated. Ofcourse, it is possible to provide a greater number of transistorswitches.

FIG. 2 graphically illustrates the function of the multipoint member oroutput selector 11. The line Xe represents the zero point, which is theoutput 13 in the region II which is associated with a normal correctlypositioned sheet means. Depending on the distance of Xa from the lineXe, each voltage potential is associated with a specific output. Theregion 1 is correlated with the output 12 for indicating an omittedsheet, the region III is correlated with a duplicate sheet, the revionIV is correlated with a triple sheet, and the region V is correlatedwith a stack of four sheets, so that regions I to V are respectivelyassociated with the outputs 12 to 16.

It can be assumed that at the measuring point normally only one sheet islocated. If the sheets are transported in overlapping condition, thestandard normal sensed thickness of the stream of sheets will be adouble sheet since portions of two successive sheets 1, l'

overlap, and consequently a single sheet must be indicated as an omittedsheet.

The embodiment of the invention illustrated in FIGS. 3, 7 and 10operates as follows: At the sensing moment, a double sheet is pushedunder the sensing roller 22, corresponding to two overlapping sheets1, 1. The elastic deformation and deflection of the sensing arm 21 istransformed by the extensible strips 24 into a resistance change in thebridge circuit of FIG. 5. By adjusting resistors 26 and 27, the bridgecircuit is balanced, and the output voltage Ua of operation amplifier 28becomes zero. The apparatus is now ready for an operation. If at thesensing moment only one sheet, or a plurality of sheets is located underthe sensing roller 22, the resistance of the extensible strips 24 isvaried, and the output voltage Ua has a different high voltagepotential. The respective voltage potential Ua is supplied to the outputselector 11 shown in FIG. 10, which, in accordance with the adjustedcharacteristic, as shown in FIG. 2, supplies a voltage signal to therespective output 12. The, adjustment of different thicknesses of thesensed sheet means is carried out by varying the bridge supply voltageUs.

The embodiment of FIG. 4 and FIG. 9 provides a signal magnitude sensormeans 8' in the form of a lever 29 having at one end an angular baffleor blocking plate 30 and at the other end a sensing roller 22. Lever 29carries a slide block 31b mounted in a housing 31a for adjustment of thelength of lever 29 by means of a clamping screw 31. Lever 29 isangularly movable about a pivot 31 so that the angular position of thebaffle plate 30 is changed when sensing roller 22 senses sheet means ofdifferent thickness due to omission or duplication of the sheet.

As also shown in FIG. 9, pressure air is supplied to an annular nozzle32a so that the stream of air is reflected and reversed to flow to thesensor tube 32, producing pressure as indicated at Pa in FIG. 4. Thepressure Pa of the reflected air is of course smaller than the pressurePe of the pressure air supplied to nozzle 32a. Depending on the sensedthickness of the stream of sheets, lever 29 is angularly displaced sothat the position of baffle plate 30 relative to the annular nozzle 32is varied. The variation of the angle causes also a variation of thepressure Pa which depends on the distance between the baffle plate 30and the nozzle 32 in accordance with the graph shown in FIG. 8. As shownin FIG. 4, the pressure Pa acts on the pneumaticelectric transducershown in FIG. 9 to produce a voltage U at the output.

The return flow tube 32 is connected by a hose 38 with a pneumatic limitelement 39 which has three air chambers. The first chamber 40 isconnected with the hose 38 and return tube 32, and separated by amembrane 42 from the second air chamber 41 which is separated by a rigidwall 44 from a third air chamber 43. Wall 44 has a nozzle 45 projectinginto the second air chamber 41 which has an outlet 46 communicating.with the ambient air. The third air chamber 43 is at the same time thefirst air chamber of the following normal pressure-low pressurepneumatic amplifier 47. Air chamber 43 is separated from the second airchamber 48 of the pneumatic amplifier 47 by a membrane 49, while thesecond air chamber 58 is separated from the third air chamber 50 of theamplifier 47 by a membrane 51. Membranes 49 and 51 are connected by arigid connector 52.

A conduit system 53 is provided in the second air chamber 48 of theamplifier 47, and extends in the direction of the connector 52,surrounding connector 52. A second conduit system 54 branches off thefirst conduit system 53, and is connected by the hose 55 with apneumatic electric transducer 56.

The conduit system 53, 54 divides the air chamber 48 of the amplifier 47into two chamber parts. The first part of air chamber 58 is connected byconduit 37 with a pressure source, and the second part of air chamber 48with the ambient air. The third air chamber 50 is also connected withthe ambient air.

A pneumatic-electric transducer 56 is constructed similar to theamplifier 47, and has a first air chamber 57 separated from a second airchamber 58 by a membrane 59. The second air chamber is separated fromthe third air chamber 60 by a membrane 61. Membranes 59, 61 areconnected by a rigid connector 62. Membrane 61 carries a contact 63connected with a voltage source, and on the opposite side of chamber 60,a second contact 64 is provided.

During operation, the baffle plate 30 is impinged by an annular streamof air from nozzle 32a to which pressure air is supplied from pressureinlet 37. Depending on the angular position of the baffle plate 30,which depends on the thickness of the sensed sheet means, the backpressure in the sensor tube 32 varies, and air at this pressure entersthrough hose 38 into the first chamber 40 of the pneumatic limit element39.

At low back pressure, corresponding in FIG. 4 to a great distance a ofbaffle plate 30 from the nozzle 32, the membrane 42 is in theillustrated position, and air supplied to the third chamber 43 can enterthrough nozzle 45 into the second chamber 41 to flow out of outlet 46.Due to the free flow, the membranes 49 and 51 are in the illustratedposition, and the air can flow, as indicated by broken lines and anarrow, through hose -55 to the pneumatic-electric transducer 56. Thepressure in chamber 41 deforms membrane 49 so that the conduit system 53is closed, and the air cannot flow to the pneumatic-electric transducer56, and the pressure at the outlets of the low pressure-normal pressureamplifier 47 is zero.

Consequently, the membrane 59 of the pneumaticelectric transducer 56returns to its initial position shown in FIG. 9, and the electriccontacts 63,64 open so that no output voltage signal is produced.

The pneumatic limit element 39 responds only to a predetermined limitpressure so that it can respond to only two signal conditionsrepresenting, for example, an omitted sheet and a correctly positionedsheet. If additionally, double sheets and triple sheets are to beevaluated, corresponding pressure limit elements, low pressuremormalpressure amplifiers, and pneumaticelectric transducers are required. Thefunction of a pneumatic-electric transducer is, for example described inthe U.S. Pat. No. 3,457,384.

Referring now to the embodiment illustrated in FIGS. 5 and 6, the signalmagnitude sensor means 8" includes a sensing piston 34 which rests onthe overlapping portions of two sheets 1 and 1'. The rear portion 34a ofsensing piston 34 is located in the light of a source of light 36 whichis directed toward a photoelectric matrix 35. Adjusting means 4" areschematically indicated by an arrow. Portion 34a, source of light 36 andphotoelectric matrix 35 constitute a signal transducer 9" whichtransforms the mechanical movement of sensing piston 34 into electricpulses at output wires 35a of the matrix 35. A thickness variation ofthe sheet means 1, 1' due to the omission of a sheet or the addition ofan unwanted sheet, is first transformed into movement of the sensingpiston 34, and in accordance with the distance of displacement of pistonportion 34a between the source of light 36'and the photoelectric matrix35, a portion of the photoelectric matrix is covered. The coveredportions of the photoelectric matrix 35 produce a different signalvoltage than the uncovered portions, and in this embodiment, the signalevaluation and output selection is accomplished by a multiplex device,not shown, of the type described in the publication Instruments andControl Systems volume 41, 1968, No. 11, page 50.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofapparatus for controlling transported sheets, differing from the typesdescribed above.

While the invention has been illustrated and described as embodied inan'apparatus and method for detecting improper feeding of transportedsheets, it is not intended to be limited to the details shown, sincevarious modifications and strucutral changes may be made withoutdeparting in any way from the spirit of the present invention. r

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledgereadilyadapt it for various applications without omitting features,that, from the standpoint of prior art, fairly constitute essentialcharacteristics of the geberic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

We claim:

1. In combination with an arrangement for transporting a stream ofsheets along a predetermined path in a predetermined manner, a systemfor detecting whether sheets are being transported along said path insaid predetermined manner, particularly for detecting the improperabsence of a sheet or the improper presence of a plurality of sheetswhere a single sheet should be provided, the arrangement comprising, incombination, sensing means positioned to sense the thickness of saidstream of sheets at least at one location along said path, and operativefor generating an analog signal having an analog value indicative of thesensed thickness; and analog-to-digital converter means having an inputconnected to said sensing means to receive said analog signal and beingoperative for determining into which of a plurality of predeterminedranges corresponding to the thicknesses of different respective numbersof sheets the analog value of said analog signal falls, and forgenerating one of a predetermined plurality of corresponding digitaloutput signals indicative of the range into which the analog value ofsaid analog signal falls, to provide an indication when a sheet isimproperly absent or when a plurality of sheets are present where only asingle sheet should be provided, wherein said sensing means comprises abendable support arm having a free end, a sensing roller mounted forrotation on said free end and held by said bendable support arm in aposition bearing down upon and contacting the sheets of said stream ofsheets, with said sensing roller and said bendable support arm being sooriented with respect to each other and with respect to said stream ofsheets that changes in the thickness of said stream effect displacementof said roller in the direction of the thickness of said sheets andresult in bending of said bendable support arm to an extentcorresponding to the displacement of said roller and corresponding tothe change in thickness of said stream of sheets, and at least onestrain-gage element mounted on said bendable support arm at such alocation as to undergo resistance changes in response to bending of saidbendable support arm.

2. A combination as defined in claim 1, and further including means forfixedly mounting the other end of said bendable support arm, said meansfor fixedly mounting being adjustable for effecting changes in thelocation along the length of said arm at which said arm is fixedlymounted.

3. A combination as defined in claim 1, wherein said at least onestrain-gage element forms part of a bridge circuit having an output andconstituting part of said sensing means, and wherein said sensing meansfurther includes and operational amplifier having an input connectedacross the output of said bridge circuit.

4. A combination as defined in claim 1, wherein said analog-to-digitalconverter means comprises a circuit having an input connected to receivesaid analog signal and having plurality of outputs and a plurality ofthreshold levels, one associated with each of said outputs, with saidlevels, establishing the limits of respective onesof said ranges andbeing associated with different multiples of the thickness of one sheetof said stream of sheet, including zero thickness and the thickness of asingle sheet.

5. In combination with an arrangement for transporting a stream ofsheets along a predetermined path in a predetermined manner, a systemfor detecting whether sheets are being transported along said path insaid predetermined manner, particularly for detecting the improperabsence of a sheet or the improper presence of a plurality of sheetswhere a single sheet should be provided, the arrangement comprising, incombination, sensing means positioned to sense the thickness of saidstream of sheets at least at one location along said path, and operativefor generating an analog signal having an analog value indicative of thesensed thickness; and analog-to-digital converter means having an inputconnected to said sensing means to receive said analog signal and beingoperative for determining into which of a plurality of predeterminedranges corresponding to the thicknesses of different respective numbersof sheets the analog value of said analog signal falls, and forgenerating one of a predetermined plurality of corresponding digitaloutput signals indicative of the range into which the analog value ofsaid analog signal falls, to provide an indication when a sheet isimproperly absent or when a plurality of sheets are present where only asingle sheet should be provided, wherein said analog-to-digitalconverter means comprises a circuit having an input connected to receivesaid analog signal and having plurality of outputs and a plurality ofthreshold levels, one associated with each of said outputs, with saidlevels, establishing the limits of respective ones of said ranges andbeing associated with different multiples of the thickness of one sheetof said stream of sheet, including zero thickness and the thickness of asingle sheet.

6. A combination as defined in claim and further including a digitalindicator device connected to said analog-to-digital converter means forproviding a digital indication of the range into which the analog valueof said analog signal falls.

7. A combination as defined in claim 5; and further including storagemeans connected to said analog-todigital converter means for recordingthe range into which the analog value of said analog signal falls,whereby to make possible subsequent analysis of the operation of saidtransporting arrangement.

8. A combination as defined in claim 5; and further including controlmeans for controlling operation of said transporting arrangement independence upon which of said predetermined plurality of digital outputsignals is generated by said analog-to-digital converter means.

9. A combination as defined in claim 8, wherein said control means isoperative for terminating the trans porting of said sheets in responseto generation by said analog-to-digital converter means of apredetermined one of said plurality of digital output signals.

10. A combination as defined in claim 5, wherein said sensing meanscomprises a mechanical sensor member so mounted with respect to saidpredetermined path as to contact said stream of sheets and be physicallydisplaced by said stream a displacement distance corresponding to thethickness of said stream, and wherein said sensing means furthercomprises transducer means responsive to the displacement of saidmechanical sensor member and operative for generating a signalindicative of the extent of such displacement and thereby indicative ofthe sensed thickness of said stream.

11. A combination as defined in claim 10, wherein said transducer meanscomprises at least one transducer element responsive to the displacementof said mechanical sensor member and also means for converting theresponse of said transducer element into said analog signal.

12. A combination as defined in claim 5, wherein said sensing meanscomprises a bendable support arm having a free end, a sensing rollermounted for rotation on said free end and held by said bendable supportarm in a position bearing down upon and contacting the sheets of saidstream of sheets, with said sensing roller and said bendable support armbeing so oriented with respect to each other and with respect to saidstream of sheets that changes in the thickness of said stream effectdisplacement of said roller in the direction of the thickness of saidsheets and result in bending of said bendable support arm to an extentcorresponding to the displacement of said roller and corresponding tothe change in thickness of said stream of sheets, and at least onestrain-gage element mounted on said bendable support arm at such alocation as to undergo resistance changes in response to bending of saidbendable support arm.

1. In combination with an arrangement for transporting a stream ofsheets along a predetermined path in a predetermined manner, a systemfor Detecting whether sheets are being transported along said path insaid predetermined manner, particularly for detecting the improperabsence of a sheet or the improper presence of a plurality of sheetswhere a single sheet should be provided, the arrangement comprising, incombination, sensing means positioned to sense the thickness of saidstream of sheets at least at one location along said path, and operativefor generating an analog signal having an analog value indicative of thesensed thickness; and analog-to-digital converter means having an inputconnected to said sensing means to receive said analog signal and beingoperative for determining into which of a plurality of predeterminedranges corresponding to the thicknesses of different respective numbersof sheets the analog value of said analog signal falls, and forgenerating one of a predetermined plurality of corresponding digitaloutput signals indicative of the range into which the analog value ofsaid analog signal falls, to provide an indication when a sheet isimproperly absent or when a plurality of sheets are present where only asingle sheet should be provided, wherein said sensing means comprises abendable support arm having a free end, a sensing roller mounted forrotation on said free end and held by said bendable support arm in aposition bearing down upon and contacting the sheets of said stream ofsheets, with said sensing roller and said bendable support arm being sooriented with respect to each other and with respect to said stream ofsheets that changes in the thickness of said stream effect displacementof said roller in the direction of the thickness of said sheets andresult in bending of said bendable support arm to an extentcorresponding to the displacement of said roller and corresponding tothe change in thickness of said stream of sheets, and at least onestrain-gage element mounted on said bendable support arm at such alocation as to undergo resistance changes in response to bending of saidbendable support arm.
 2. A combination as defined in claim 1, andfurther including means for fixedly mounting the other end of saidbendable support arm, said means for fixedly mounting being adjustablefor effecting changes in the location along the length of said arm atwhich said arm is fixedly mounted.
 3. A combination as defined in claim1, wherein said at least one strain-gage element forms part of a bridgecircuit having an output and constituting part of said sensing means,and wherein said sensing means further includes and operationalamplifier having an input connected across the output of said bridgecircuit.
 4. A combination as defined in claim 1, wherein saidanalog-to-digital converter means comprises a circuit having an inputconnected to receive said analog signal and having plurality of outputsand a plurality of threshold levels, one associated with each of saidoutputs, with said levels, establishing the limits of respective ones ofsaid ranges and being associated with different multiples of thethickness of one sheet of said stream of sheet, including zero thicknessand the thickness of a single sheet.
 5. In combination with anarrangement for transporting a stream of sheets along a predeterminedpath in a predetermined manner, a system for detecting whether sheetsare being transported along said path in said predetermined manner,particularly for detecting the improper absence of a sheet or theimproper presence of a plurality of sheets where a single sheet shouldbe provided, the arrangement comprising, in combination, sensing meanspositioned to sense the thickness of said stream of sheets at least atone location along said path, and operative for generating an analogsignal having an analog value indicative of the sensed thickness; andanalog-to-digital converter means having an input connected to saidsensing means to receive said analog signal and being operative fordetermining into which of a plurality of predetermined rangescorresponding to the thickNesses of different respective numbers ofsheets the analog value of said analog signal falls, and for generatingone of a predetermined plurality of corresponding digital output signalsindicative of the range into which the analog value of said analogsignal falls, to provide an indication when a sheet is improperly absentor when a plurality of sheets are present where only a single sheetshould be provided, wherein said analog-to-digital converter meanscomprises a circuit having an input connected to receive said analogsignal and having plurality of outputs and a plurality of thresholdlevels, one associated with each of said outputs, with said levels,establishing the limits of respective ones of said ranges and beingassociated with different multiples of the thickness of one sheet ofsaid stream of sheet, including zero thickness and the thickness of asingle sheet.
 6. A combination as defined in claim 5; and furtherincluding a digital indicator device connected to said analog-to-digitalconverter means for providing a digital indication of the range intowhich the analog value of said analog signal falls.
 7. A combination asdefined in claim 5; and further including storage means connected tosaid analog-to-digital converter means for recording the range intowhich the analog value of said analog signal falls, whereby to makepossible subsequent analysis of the operation of said transportingarrangement.
 8. A combination as defined in claim 5; and furtherincluding control means for controlling operation of said transportingarrangement in dependence upon which of said predetermined plurality ofdigital output signals is generated by said analog-to-digital convertermeans.
 9. A combination as defined in claim 8, wherein said controlmeans is operative for terminating the transporting of said sheets inresponse to generation by said analog-to-digital converter means of apredetermined one of said plurality of digital output signals.
 10. Acombination as defined in claim 5, wherein said sensing means comprisesa mechanical sensor member so mounted with respect to said predeterminedpath as to contact said stream of sheets and be physically displaced bysaid stream a displacement distance corresponding to the thickness ofsaid stream, and wherein said sensing means further comprises transducermeans responsive to the displacement of said mechanical sensor memberand operative for generating a signal indicative of the extent of suchdisplacement and thereby indicative of the sensed thickness of saidstream.
 11. A combination as defined in claim 10, wherein saidtransducer means comprises at least one transducer element responsive tothe displacement of said mechanical sensor member and also means forconverting the response of said transducer element into said analogsignal.
 12. A combination as defined in claim 5, wherein said sensingmeans comprises a bendable support arm having a free end, a sensingroller mounted for rotation on said free end and held by said bendablesupport arm in a position bearing down upon and contacting the sheets ofsaid stream of sheets, with said sensing roller and said bendablesupport arm being so oriented with respect to each other and withrespect to said stream of sheets that changes in the thickness of saidstream effect displacement of said roller in the direction of thethickness of said sheets and result in bending of said bendable supportarm to an extent corresponding to the displacement of said roller andcorresponding to the change in thickness of said stream of sheets, andat least one strain-gage element mounted on said bendable support arm atsuch a location as to undergo resistance changes in response to bendingof said bendable support arm.